The safety aspect plays a crucial role in connection with the supply of electrical consumers, in particular of electric vehicles. A technique is known in which a supply device, which in particular can be the charging station for an electric vehicle, is fitted with a plurality of different components, the individual function of which is described in the following:
First of all however, the supply device must have an energy quantity meter also known as an “electricity meter”, with which the amount of electrical energy drawn from the energy supply company is detected and made available for further billing.
Such meters detect the phase current respectively provided in the mains electricity network, and the applied voltage. From this, they use multiplication and integration over time to determine the active energy quantity used expressed in units of Kilowatt hours.
The most widespread of these are so-called “Ferraris meters”, which work according to the induction principle. According to this, the single phase or multiphase alternating current together and the mains voltage induce a rotating magnetic field in an aluminium disc, generating a torque in the disc due to eddy currents. This torque is proportional to the vector product of current and voltage. The aluminium disc runs in an eddy current brake consisting of a permanent magnet, which generates a braking moment proportional to the velocity. As a result, the aluminium disc, a section of the edge of which is visible from the outside through a window, has a velocity that is proportional to the active electrical power. The aluminium disc has a roller type meter associated with it, so that the energy throughput can be read off as a numerical value in kilowatt hours (kWh).
In the case of paying customers, for example those in private households, such electromechanical energy meters with two or more counters are used, in order to charge at different rates depending on the time of day. Switching takes place between these counters, for example by means of inbuilt or external ripple control receivers, which are controlled by central ripple control systems at the energy supply company's premises. In this way the energy consumption can be charged to the consumer at a cheaper rate in periods of low network loading, for example at night.
Other devices already know are digital electronic energy meters (so-called “SmartMeters”), which contain no mechanically mobile elements.
The current is detected by means of current transformers, for example with a soft magnetic toroidal core or a current measuring system with Rogowski coils, by means of a shunt resistance or using Hall elements. The charge for the energy consumed is calculated using an electronic circuit. The result is fed to an alphanumeric display, e.g. a liquid crystal display (LCD). Digital electronic energy meters have the particular advantage of being able to be read remotely and therefore make the annual reading that has been customary up to now redundant, since the meter data are transmitted electronically, for example over the internet, to the electricity provider.
Various forms of data interfaces for data transmission to the charging unit of the energy supply company are in use, e.g. infrared, SO-interface, M-Bus, zero-potential contact, EIB/KNX, or power line communication (PLC), in which the data are transmitted via the normal mains supply line.
In addition, as is known, a supply device for a consumer has monitoring devices, in order to guarantee their proper operation and, if necessary, to initiate appropriate protective measures in the event of overload of the supply device. With regard to their functionality, this involves switching means, which serve to connect or disconnect the consumer power circuit, fusing means, which are intended to protect the electrical circuits against damage due to excessive heating of the cables or short circuits, and fault current monitoring devices.
A switching means is constructed in a known manner as an electromagnetically activated switch (“trip switch”), in which a control current flows through a magnetic coil, the magnetic attraction mechanically activating a contact that closes the main electrical circuit. As long as the control current is flowing the switch is maintained in the closed position. Trip switches differ from relays in having higher switching powers.
Types of known residual current monitoring devices are in particular so-called FI switches (also known as RCD “Residual Current protective Devices”), which in the event of a defined difference current level being exceeded (in domestic systems typically 30 Ma), disconnect the current monitored circuit from the remaining network across all poles, i.e. with respect to all except the protective conductor.
To effect this, the RCD compares the level of the outgoing current with that of the return current. The signed sum of all currents flowing through the RCD in an intact system must be equal to zero. The comparison is carried out in a summing current transformer, which adds together all currents flowing to and from the consumer with their appropriate signs. If a current is being diverted to earth somewhere in the electrical circuit, then the sum of outgoing and return current in the summing current transformer is non-zero: a current difference ΔI, which causes the triggering of the RCD and therefore the current supply to be switched off.
Fault current protection devices of type AC (AC-sensing) only detect sinusoidal fault currents. In practice therefore, pulsed-current sensing fault current protection devices of so-called “Type A” are commonly used. These detect both purely sinusoidal alternating currents and pulsing DC fault currents. This additional sensing capability is obtained by means of special magnetic materials for the toroidal tape cores that are used. Pulsed-current sensitive fault current protection devices work independently of the mains voltage.
Hardware components of the power electronics, such as e.g. frequency converters, rectifiers, uninterruptible power supplied (UPS), switch network parts or phase angle controllers, generate a bipolar, pulse-width modulated output voltage, which has switching frequencies in the range of up to 20 kHz. In case of a fault, these hardware components can also cause—as well as 50 Hz AC and DC-pulse fault currents—smooth DC fault currents and AC fault currents with a very wide range of frequencies, as well as mixed frequencies (in the case of frequency converters e.g. the switching frequency and output frequency). FI protection switches of Type A cannot accurately detect these fault currents, so that proper triggering of the FI-protection switch is not guaranteed to occur. Therefore, according to VDE 0160/EN 50178 “Equipping of heavy duty electrical systems with electronic hardware components”, paragraph 5.2.11.2 and 5.3.2.3 for protection in the event of direct and indirect contact, an RCD of “Type B” is to be used, if an electronic component of an electrical system can generate a steady DC fault current in the fault condition.
Such so-called all-current sensitive fault current protection switches (“Type B”) contain a second summing current transformer for detecting steady DC fault currents. An electronic unit transmits the switch-off command to the triggering device in the event of a fault. Monitoring for DC fault currents takes place in a manner that is independent of the mains voltage. Such a device therefore requires a supply voltage, which is tapped off the external supply lines and where appropriate the neutral line. The pulsed-current sensitive part of the switch is independent of this and works independently of the mains voltage, as in the case of Type A.
Fault current protection switches of the type described require sensors for highly accurate detection of the current and for subsequent processing of the measurement signal. In addition, regulations prescribe that FI switches in must be tested at specified time intervals. To do this, they are either activated manually or by additional devices provided for the purpose.
Finally, as a third component in a monitoring device of a supply device, excess current protection devices in the form of transmission line protection switches (LS switches or MCB “Miniature Circuit Breakers) are known. Transmission line protection switches are reusable, non-self activating resetting fuse elements, which switch off the electrical circuit automatically if an overload occurs. Devices of this kind protect transmission lines against damage due to overheating, which would result from the excess current flowing over an extended period.
An excess current can be caused by an overload or a short-circuit. If this is triggered in the event of overload, disconnection occurs if the specified nominal value of the current flowing through the transmission line protection switch is exceeded over an extended period of time. The time until triggering depends on the strength of the excess current—at high excess current it is shorter than it is for small excesses of the nominal current. To effect the triggering a bimetallic strip is used, which bends when heated by the flowing current and triggers the switch-off mechanism. The response time of an excess current protection device at different current strengths is termed the characteristic and is represented in current-time curves.
In the event of a short-circuit occurring in the system, a very rapid triggering, usually within a few milliseconds, must take place by means of an electromagnet in the transmission line protection switch that has current flowing through it. This requires sensors for the appropriate detection and circuit components for further processing of the measurement signal. Transmission line protection switches can also be manually triggered, e.g. for maintenance work or for temporary service shutdowns. For this purpose, a toggle switch or a triggering button is located on the front face of the switch.
Another known method is to combine a transmission line protection switch with an FI module, in order to obtain a situation whereby during the detection of a fault current situation by the FI module a transmission line shutdown can take place via the transmission line protection switch.
The monitoring and fuse protection devices described above are used in practice in the form of the individual components described in a variety of ways. For example, individual electrical circuits or consumer branches, which include a large number of different electrical consumers, each fuse-protected by appropriately dimensioned components. In this arrangement, in different branches appropriate approaches to the dimensioning of the components are applied, mostly involving a hierarchical fusing design. This means fusing is also effected at different voltage levels of a network such that they are separate from one another.
The problem addressed by the present invention on the other hand is to develop a monitoring and safety design, which is suitable for such an application in which a single electrical energy consumer is to experience a fusing system specially customised to its consumer circuit, independent of other consumers.